1. Field of the Invention
The invention relates to regulating the flow of fuel and secondary induced air to an aspirating burner mounted in a firetube during operation of the burner and when the burner is shut down. More specifically, the invention relates to automatic regulation of a damper controlling air flowing into a firetube during burner operation and shutdown.
2. Description of the Prior Art
The relation of excess air flow to the thermal efficiency of a combustion process is well known. It was not surprising, when investigating aspirating burners for which secondary air is not controlled, to find excess air increasing to as much as 250% at low firing rates. The gross thermal efficiency of these uncontrolled systems ranges from 62% at high firing rates to 50% at low firing rates.
Low efficiency, due simply to excess air, cannot be tolerated during the present energy shortage. But, this is not the only problem. When the aspirating burner system is temporarily shut down, ambient air is drawn by the exiting heated air through the firetube and cools the fluid being heated by the burner system. This drafting through the firetube is a further loss of energy which is now in critically low supply.
The present technology calls for control of secondary air to the aspirating burner mounted in a firetube. First, automatic control of secondary air to raise the thermal efficiency over the entire range of burner operation is required. Second, control of the drafting through the firetube during the shutdown periods of intermittent firing is also demanded.